The broad, long term objective of this proposal is to identify a clinically useful, noninvasive method of screening for carotid artery stenosis secondary to atherosclerotic disease. Stroke affects nearly 400,000 Americans each year and is the third leading cause of death in the United States. Carotid endarterectomy decreases the risk of further strokes in symptomatic patients with greater than 70% maximum diameter stenosis (MDS) and may benefit asymptomatic patients as well. Better noninvasive screening for identification of extracranial carotid artery stenosis is important to identify patients at high risk for future cerebral infarction. Our specific aim is to determine the suitability of magnetic resonance angiography (MRA) for noninvasive screening for carotid artery stenosis, a technology assessment study. Intra-arterial (IA) carotid angiography is the current gold standard for carotid evaluation. Our first hypothesis is that, in symptomatic patients, MRA agrees with IA angiography of the carotid bifurcation at least as well as duplex carotid ultrasonography (US), the current noninvasive screening examination. Our second hypothesis is that carotid siphon stenosis on MRA correlates with IA angiography, the gold standard. A total of 157 patients (314 carotid arteries) will be enrolled in this prospective, cross-sectional study. Each patient will undergo MRA, US, and IA angiography of the carotid bifurcation and MRA and IA angiography of the carotid siphon. Twenty asymptomatic, age-matched controls will undergo carotid MRA and US to look for trends in screening asymptomatic patients. Three blinded neuroradiologists will measure the % MDS on the MRA and IA angiograms. Two blinded ultrasonographers will measure % MDS on the US. The validity of the two hypotheses will be statistically tested. MRA and US reproducibility as well as intraobserver and interobserver variability will be evaluated in order to apply the study findings to usual clinical practice. All symptomatic and asymptomatic study subjects will have a two year clinical follow-up. Preliminary results are promising for MRA to become the method of choice for noninvasive screening for atherosclerotic carotid artery stenosis.